1. Field of the Invention
The present invention relates to a pneumatic tire which aims for an improvement in performances on wet roads and in performances on snowy and icy roads.
2. Description of the Related Art
Pneumatic tires are conventionally provided with sipes in the surfaces of blocks formed on the tread surface. Such tires aim to improve driving performances/braking performances and directional stability on wet road surfaces and snowy and icy road surfaces by increasing the edge effect so as to improve the water drainability.
However, when a large number of sipes which are opened onto the both side surfaces are provided in a block, the problem arises that the rigidity of the block decreases to deteriorate directional stability. Closed sipes, neither of whose ends opens onto grooves, are effective in order to ensure the rigidity of the block. But water cannot drain from the end portions of the sipes into grooves, and thus the problem that drainability is inferior arises.
The present invention was developed in order to overcome the above-described drawbacks, and an object of the present invention is to provide a pneumatic tire which aims for an improvement in performances on wet roads and performances on snowy and icy roads by improving drainability while maintaining block rigidity.
In order to achieve the above object, the present invention has the following aspects.
A first aspect of the present invention is a pneumatic tire comprising: a tread surface having a plurality of grooves formed therein which intersect one another, thereby defining a plurality of land portions that each have a ground contacting surface and side surfaces; and at least one water drainage passage provided in the land portion, wherein the water drainage passage is a hole (a communicating hole) formed inside the land portion, the hole has two ends, one end is opened at the ground contacting surface of the land portion, and the other end is opened at the side surface of the land portion.
In accordance with the first aspect, when water is taken-in into the water drainage passage from the portion which is opened at the ground contacting surface, even if the hole of the opening portion at the ground-contacting surface closes up by deformation of the block-shaped land portion due to the block-shaped land portion contacting the road surface, the water within the water drainage passage (the hole) can be discharged, via the hole, to a groove by the opening end at side surfaces.
Because only the hole, which passes through the interior, is formed as the water drainage passage at the block-shaped land portion, sufficient rigidity of the water drainage passage can be maintained as compared with a block-shaped land portion which is formed with a sipe which is opened at both ends or one end in the contacting surface.
Namely, the drainability of the water drainage passage can be improved without lowering the block rigidity, and the ground contacting ability of the block-shaped land portion can be improved by the improvement in the water drainability. Thus, the performance on wet roads and the performance on snowy and icy roads can be markedly improved.
In a second aspect of the present invention, the water drainage passage is a hole having a circular or oval cross-section.
In accordance with the second aspect, the cross-section of the hole, which communicates from the ground-contacting surface of the block-shaped land portion to side surface thereof, is circular or oval. Thus, a concentration of stress in the hole can be prevented by those rounded cross-sectional shapes. Accordingly, generation of cracks at the hole due to deformation of the block-shaped land portion can be suppressed.
In a third aspect of the present invention, the cross-section of the hole is a thin, elongated configuration having a longitudinal direction and a transverse direction.
In accordance with the third aspect, the opening end of the hole at the ground-contacting surface is a thin, elongated configuration having a longitudinal direction and a transverse direction. Therefore, the longitudinal direction of the opening end becomes an edge component, and contributes to directional stability and braking performance.
In a fourth aspect of the present invention, the hole has a curved portion or a bent portion from the ground-contacting surface toward the side surface.
In accordance with the fourth aspect, by providing a curved portion or a bent portion in the hole, concentration of stress at specific portions can be prevented, and the generation of cracks and the like can be suppressed. The xe2x80x9ccurved portionxe2x80x9d is a portion which is formed in a continuous curve, and the xe2x80x9cbent portionxe2x80x9d is a portion bent so as to include an obtuse angle.